The Transgenic Mouse Shared Resource (TMSR) provides a variety of services to Cancer Center investigators for the production and maintenance of transgenic and knockout mice. The services include production of transgenic mice by oocyte injection, production of gene targeted mice by embryonic stem (ES) cell injection, freezing of embryos, rederivation of embryos to eliminate pathogens; culturing ES cells for gene targeting experiments; and assisting with genotyping and husbandry of clients' mice. In addition, TMSR currently maintains two specialized transgenic lines that express Cre or FIp in the germline for genetic manipulation of transgene/knockouts in vivo. TMSR has a fully equipped embryo manipulation laboratory in the Borwell animal facility and an adjoining four-room suite of mouse husbandry rooms. Since its inception in 1999, this Resource has produced 93 transgenic founder mice from 28 constructs, has successfully targeted ES cells with 33 constructs, and has successfully transmitted these ES cell lines through the germline to produce knockout mouse strains. In addition, five ES cell clones cultured by other laboratories at Dartmouth have been used to produce chimeric mice that transmitted the ES cell genome through the germline. The facility has frozen six strains and rederived 12 strains. Use of this Resource by NCCC researchers is expanding rapidly, and it is predicted that 20 constructs will be successfully used to make transgenic mice and 12 knockout mouse lines will be made in the next year. Further increases in the use of the TMSR are anticipated with recruitment of new faculty to the Cancer Center.